Maximizing power system stability through wide area protection

The electrical power system is becoming more and more complex with the increasing demand of the electricity across the world, as the world is becoming the global village. The electrical power system must be reliable and safe enough to fulfil the energy requirements with the continuous supply of energy. The chances of power system's blackouts and outages are increasing with its increased complexity. So, there is a need of an efficient control system to make the power system more safe, efficient and reliable. Wide Area Monitoring, Protection and Control system (WAMPAC) is becoming an emerging technology for an efficient monitoring, protection and control of power system. Phasor measurement unit (PMU) is an integrated part of wide area monitoring, protection and control (WAMPAC) system, which can be used for monitoring, protection and control of complex electrical power systems. PMU gives the synchronized phasor measurements of voltage and current and can easily monitor and control even small disturbances in power system to protect the power system from any blackouts and outages before any fault occurs. In the proposed paper a PMU model is designed in MATLAB/Simulink and then PMU is used for power system protection and the comparative analysis are done with the conventional protection technique for an interconnected two-area network power system.

Several major blackouts in the past have shown the need for advanced wide‐area monitoring and control (WAMC) techniques. Advanced synchrophasor visualization and monitoring can be realized with time‐referenced power system data that are collected by phasor measurement units (PMUs) using synchronized clocks. Presently, PMUs are being deployed around the world at a rapid rate for various power system applications. When a necessary number of PMUs are installed at optimal locations throughout the network, the complete state of the system can be observed. PMUs take real‐time measurements to determine the state of the power system and can be used to enhance state estimation efficiency. With PMUs in place, there are many control and protection schemes that can be implemented successfully to take preventive and corrective actions. These remedial action schemes (RASs) are classified by the IEEE Power System Relaying Committee (PSRC) as system integrity protection schemes (SIPSs). This work involved the development of a real‐time hardware test bed in order to analyze the transient stability of a simulated power system by using synchrophasors to visualize system stress across a transmission line with and without load‐shedding schemes. The real time digital simulator (RTDS®) was used to model the power system in real time. PMUs, a satellite‐synchronized clock, and a synchrophasor vector processor (SVP) were used to test the synchrophasor application. Copyright © 2010 John Wiley & Sons, Ltd.

Applied in WAMS, phasor measurement units (PMU) have proved their effectiveness in increasing distributed power systems reliability. In recent years, devices performing synchrophasor measurements have found application in various systems serving to increase reliability and efficiency of power systems, e.g. by means of improving the quality of system state estimation [1]–[4]. Wide Area Control Systems (WACS), Wide Area Protection Systems (WAPS), Wide Area Monitoring, Protection And Control Systems (WAMP ACS) are some promising fields of application for this class of devices.

Electrical power system monitoring, protection, operation, and control schemes are undergoing significant changes toward the next generation fully automated, resilient, and self-healing grids. At present, there still exists a lack of available user-friendly tools for the synchronized measurement technology supported application design. This paper presents a synchro-measurement application development framework (SADF) to promote a simplified design and thorough validation of synchro-measurement (IEEE Standard C37.118.2-2011) supported user-defined applications under realistic conditions. The proposed SADF supports online receiving of a phasor measurement unit (PMU) or phasor data concentrator (PDC) provided data stream and enables simultaneous use of processed machine-readable synchro-measurements in advanced user-defined applications. This paper fills the scientific gap between the IEEE Standard C37.118.2-2011 specifications and its implementation by proposing a novel robust communication technique and efficient synchro-measurement data parsing methodology. As a proof of concept, the proposed SADF is implemented as a novel open-source MATLAB library. Combining this library with MATLAB’s signal processing and visualization functions allows mastering the design and validation of complex wide-area monitoring, protection, and control applications, as well as PMU/PDC performance and compliance verification. Finally, this paper verifies the proposed library against the standard specifications, assesses its interoperability and performance via a cyber-physical simulation platform, and presents online voltage magnitude monitoring as an example application.

Monitoring and controlling of large power systems is becoming more challenging as a consequence of the growth of their size, increasing demand for electricity, penetration of variable renewable energy sources, uncertainty in many operating parameters, and the growing number of interconnections. Therefore, system operators feel the need for a real-time wide area monitoring, protection and control system that provides more accurate information about the state of the power system and assists operators in the implementation of corrective actions to operate at high levels of security and reliability and to respond rapidly to disturbances. Synchronized measurement technology, which allow taking synchronized measurements from widely dispersed locations, has made possible the development of real-time wide area monitoring systems. At present, phasor measurements units (PMUs) are the devices most used for power system monitoring. When a PMU is placed at a bus, it can provide an accurate measurement of the voltage phasor (magnitude and angle), as well as the current phasors through the incident transmission lines.

Power systems and especially Smart Grids increasingly apply Information and Communication Technologies (ICT) for exchanging information over wide area networks. Here, the performance of the ICT has become crucial for the development of new Wide Area Monitoring, Protection And Control (WAMPAC) [1] systems. In this context, simulations are a common way for evaluation, but power systems and communication networks are usually analysed with dedicated simulators. Therefore a combined simulation for analysing the dynamics and mutual impacts of both domains is needed. In this paper we present a generic hybrid simulation architecture based on the IEEE standard 1516 - High Level Architecture [2] to enable a combined simulation of power systems and communication networks in an integrated simulation environment. First, we introduce our hybrid simulator architecture, along with the communication and synchronization process between sub-simulators. Secondly, we present our communication networks architecture for modelling the network traffic caused by the information transmitted by control and protection algorithms within the electrical transmission system. Finally, we introduce our modelling approach for mapping entities between the power systems and the communication networks. For this purpose, we introduce our concept of a Substation Data Processing Unit, which represents entities on substation level by providing an IEC 61850 [3] based model for mapping logical functions for local process control, implementing decentralized protection and control algorithms and providing additional components for the power systems (e.g Phasor Measurement Units (PMUs) [4]).

Remedial Action Schemes (RAS) provide automatic control action with high impact on system performance. In order to improve the resilience of the RAS against any single node failure and to guarantee the secured and reliable operation of the power systems, distributed implementations of the RAS is researched upon. The input data to such a distributed RAS must be of high quality. In addition, RAS operation must be fast. Traditional centralized state estimation, which feeds data to RAS is slow and cannot meet the requirements of RAS. New approach needs to be developed to provide the fast and accurate data to RAS. In order to solve this problem, distributed state estimation is developed as an alternative strategy to feed data to the RAS. This paper discusses the implementation of Distributed Linear State Estimation (DLSE) in a decentralized platform called Resilient Information Architecture Platform for Smart Grid (RIAPS). The DLSE algorithm is fully implemented in RIAPS platform and validated on a real-time testbed consisting of Real Time Digital Simulator, Phasor Measurement Units and BeagleBones. The effectiveness of the proposed approach is validated through online simulations on IEEE 14-bus test system under various cyber failures.

The wide area measurements systems (WAMS) play a vital role in the operation of smart grids. The phasor measurement units (PMU) or synchrophasors are one of the principle components under WAMS. PMU in a smart grid converts power system signals into phasor from voltage and current which enhances the observability of the power system. A variety of operations is performed by the PMUs such as adaptive relaying, instability prediction, state estimation, improved control, fault and disturbance recording, transmission and generation modeling verification, wide area protection and detection of fault location. The PMUs can improve the performance of grid operations and monitoring. Thus, PMU optimization is very necessary to achieve the desired power system observability. The performance of the PMUs can be optimized using artificial intelligence (AI) technologies. The novice method of monitoring maximum power transfer using PMUs equipped with artificial neural networks has been discussed in this paper. In this paper, a two-bus system model is developed that can be generalized to multiple bus systems. The proposed method is novel, simple, feasible, and cost effective for smart grids.

Wide-area backup protection and protection performance analysis scheme using PMU data

In recent years several catastrophic power systems blackouts have occurred worldwide. Various reasons have been declared for these failures. Economical limitations due to power system restructuring restrictions, inadvertent operation of protective relays and inefficient design of conventional load shedding schemes are of the most important reasons causing these blackouts. In fact, due to both economical and technological restrictions, it is not possible to completely prevent these blackouts. However, with the aid of some protection and control strategies, frequency and intensity of these blackouts may be reduced. One of the important protection strategies used for this purpose is a class of protection schemes known as ‘System Protection Schemes’ or ‘Wide Area Protection Schemes’. One of the most commonly used types of system protection schemes, generally accepted after the north-eastern blackout of 1965, is Under Frequency Load Shedding (UFLS) scheme. Conventional under frequency load shedding scheme is designed to retrieve the balance of generation and consumption following a disturbance. In the conventional load shedding method frequency settings, time delay settings and the amount of load to be shed in each step are constant values. The loads to be shed by this scheme are also constant load feeders and are not selected adaptively. Using this constant non-adaptive load shedding algorithm is not the most efficient scheme for all power system disturbances. In some combinational disturbances, events causing frequency to drop are followed by other events causing voltage drop. In these cases, since loads are voltage dependent, total system load is reduced and system frequency might not decrease so much to activate UFLS relays. However, the system could eventually collapse due to voltage instability. In many such cases the system would survive if the load shedding relays operate adaptively and appropriately. For example if for large disturbances, higher frequency settings and lower time delays are used adaptively, a faster load shedding response is obtained and as a result system collapses may be prevented. In this paper a new UFLS algorithm is proposed. The purpose of this algorithm is to adaptively adjust speed of load shedding based on the magnitude of disturbance. In this method rate of frequency decline is used as a criterion to determine intensity of disturbance. Thereby, for large disturbances higher frequency settings and lower time delays are used. Application of the proposed algorithm to the simulated model of Khorasan network in Iran confirms its satisfactory performance. As the results of simulations show, several voltage collapse instabilities may be prevented by using the proposed adaptive UFLS method.

Closed-loop distribution network can improve power supply reliability and adapt to the injection of DGs. However, problems such as power flowing in both directions have brought challenges to protection and control. A wide area protection and control scheme based on information sharing is proposed, which includes wide area protection control devices and integrated distribution terminals. The scheme uses extensible differential protection principle and load resection method based on load sensitivity to realize adaptive protection and self-healing control for closed-loop distribution network. Finally, the wide area protection and control scheme is compared with the traditional scheme. It shows that the wide area protection and control scheme is feasible, controllable and detectible. In addition, the wide area protection and control scheme has economic advantages such as less space and operation maintenance workload.

Phasor Measurement Units (PMU) are becoming a basic building block of modern wide area power system protection, monitoring and control schemes. Such systems rely on accurate time synchronized measurements. PMU operation is governed by the IEEE C37.118 standard. The standard sets out the performance requirements for valid phasor measurements under steady state conditions, but does not specify the response of PMUs under transient system conditions. Since most events requiring action by protection and control systems arise from transients it is important that PMUs report these anomalies in an understood and universal manner. This paper discusses the problem of determining phase during a transition from one cyclic state to another.

The pursuit of achieving total power network observability in smart grids using Phasor Measurement Units (PMUs) carries a significant promise of real-time Wide-Area Monitoring, Protection, and Control (WAMPAC). PMU applications eliminate periodical measurements, thereby increasing accuracy through a high sampling rate of the measured power systems quantities. The high costs of installation of PMUs for total power system observability presents a challenge in the implementation of PMUs. This is due to the expensive costs of PMU devices. This has led to a prominent optimal PMU placement (OPP) problem that researchers tirelessly aim to solve by ensuring a complete power network observability while using the least installed PMU devices possible. In this paper, a novel Binary Firefly Algorithm (BFA) based on the node degree centrality scores of each bus is proposed to minimize PMU installations. The BFA solves the OPP problem in consideration of the effect of Zero Injection Buses (ZIBs) under normal operation and single PMU outage (SPO). The robustness and efficiency of the proposed algorithm is tested on IEEE-approved test systems and visualized with a force-directed technique on an undirected power network graph. The proposed BFA yields the same but better optimal PMU numbers, obtained by existing meta-heuristic optimization techniques found in the literature for each of the IEEE test cases, as well as highlighting the cost–benefit of having a robust system against single PMU loss while considering the ZIB effect for an improved system measurement availability.

Optimal PMU placement for power system observability using BICA, considering measurement redundancy

SUMMARYThis paper considers the problem of placing additional phasor measurement units (PMUs) and communication links into a PMU network in a power system. The objective is for the synchrophasors (PMU outputs) across the power system to meet a prescribed availability profile with fewest new PMUs and links among them. Achieving a required synchrophasor availability profile is critical in supporting wide area monitoring, protection, and control in a power system. In our recently reported work, synchrophasor availability is solved from a controlled Markov chain where binary variables indicating placement decisions are embedded as stationary control variables. In this paper, the assumption that communication links are always available wherever needed is removed. Random interruptions in PMU communications are modeled in such a way that the reformulated placement problem remains Boolean‐convex, and the computational complexity with respect to the number of buses remains O(n2). The solution to placement of PMUs and communication links into the Institute of Electrical and Electronics Engineers (IEEE) 118‐bus test system is presented. Copyright © 2013 John Wiley & Sons, Ltd.